Adhesion of hydrophilic layers on polyester film

ABSTRACT

The adhesion of hydrophilic layers on a dimensionally stable polyester film support is improved by applying after longitudinal stretching of the polyester film a single adhesive layer thereon. The thus covered polyester film is stretched in transverse direction and heat-setted at 180*-220*C. The adhesive layer comprises 30 to 80 % by weight of a chlorine-containing copolymer, 5 to 30 % by weight of gelatin, 5 to 40 % by weight of a plasticizer for the gelatin and 0 to 30 % by weight of a metalcomplexing antistatic agent. The polyester film may be a film of polyethylene terephthalate and the hydrophilic layer applied to the single adhesive layer may be a light-sensitive gelatin silver halide emulsion layer.

United States Patent [191 Van Paesschen et al.

[ ADHESION OF HYDROPHlLlC LAYERS ON POLYESTER FILM [75] Inventors: August Jean Van Paesschen,

Antwerp; Lucien Janbaptist Van Gossum, Kontich; Jan Jozef Priem, Mortsel, all of Belgium [73] Assignee: Agfa-Gevaert N.V., Mortsel,

Belgium [22} Filed: May 24, 1973 [21] Appl. No.: 363,390

3.432,59| 3/[969 Hefflefinger I 17/7 Oct. 7, 1975 Primary ExaminerNorman G. Torehin Assistant Examiner-J. P, Brammer Attorney, Agent, or Fi'rmWilliam J. Daniel [57] ABSTRACT The adhesion of hydrophilic layers on a dimensionally stable polyester film support is improved by applying after longitudinal stretching of the polyester film a single adhesive layer thereon. The thus covered polyester film is stretched in transverse direction and heatsetted at l80220C. The adhesive layer comprises 30 to 80 by weight of a chlorine-containing copoly met, 5 to 30 by weight of gelatin, 5 to 40 by weight of a plasticizer for the gelatin and 0 to 30 by weight of a metalcomplexing antistatic agent.

The polyester film may be a film of polyethylene terephthalate and the hydrophilic layer applied to the single adhesive layer may be a light-sensitive gelatin silver halide emulsion layer,

10 Claims, No Drawings ADHESION OF HYDROPHILIC LAYERS ON POLYESTER FILM This invention relates to a method for improving the adhesion of hydrophilic layers on dimensionally stable polyester film supports, especially for improving the adhesion of hydrophilic photographic layers on films of dimensionally stable polyethylene terephthalate, and to the composite films and photographic materials thus obtained.

In order to ensure a perfect adhesion of hydrophilic layers such as photographic light-sensitive emulsion layers to dimensionally stable polyester film supports, i.e., polyester films that have been biaxially stretched and heat-setted, it is known to apply several intermediate layers between the support and the light-sensitive emulsion layer. In most cases two intermediate layers are needed. A first one, the adhesive layer, shows a good adhesion to the polyester film and at the same time possesses good attaching properties in respect of the second layer, the subbing layer, which usually is formed to a great extend of a hydrophilic colloid such as gelatin.

It is known that the adhesion of the adhesive layer to the polyester film support can be promoted by different expedients, which can be used separatedly or in combination:

the use of chlorine-containing copolymers as binding agents for the adhesive layer;

- the application of the adhesive layer before the stretching and heat-setting of the polyester film support, the latter occurring at a temperature of about 200C;

the addition to the coating solution of compounds,

generally organic solvents, which attack the polyester film surface superficially.

Although such an adhesive layer attaches itself very tenaciously to a dimensionally stable polyester film support, a supplemental subbing layer is still needed. Indeed, the adhesion of a photographic gelatincontaining layer directly to the hydrophobic adhesive layer leaves much to be desired. This confirms the general rule that a good adhesion ofa gelatin layer to a by drophobic film surface can only be obtained when the surface of the hydrophobic film has been covered with a subbing layer that contains a sufficient amount of gelatin.

It is the object of the present invention to provide a single adhesive layer combining the properties of the usual two-layer subbing combination. In this single layer chlorine-containing copolymers are present as binder material so that a perfect adhesion on the polyester film support is obtained. Moreover, the single adhesive layer contains a sufiicient amount of gelatin, so that photographic emulsion layers containing gelatin will also readily adhere to the adhesive layer.

As indicated above, in all circumstances the adhesion of the adhesive layer to the polyester film support can be improved by heating the support and the adhesive layer together at a temperature of about 200C. In

practice this can only be done when the adhesive layer is applied after longitudinal stretching of the polyester film. The thus coated polyester film is stretched then to the desired extent in transverse direction and heatsetting is effected, while keeping the film under tension, at a temperature of about 200C.

It is also known that a polymer or a product of low molecular weight can only be stretched when the temperature during stretching is higher than the softening point of the polymer or product of low molecular weight. Stretching of polyester film normally occurs at about C. Since gelatin does not have a measurable softening point, it is impossible to stretch a dry layer of gelatin at this temperature of 80C. When a layer solely consisting of a mixture of gelatin and of a chlorinecontaining copolymer is stretched, hazy layers are formed always. This can only be due to the fact that the miscibility of gelatin and of the chlorine-containing polymer is not sufficient to make sure that the presence of the stretchable polymer will favourably influence the stretchability of gelatin.

It is an object of the invention to provide hydrophilic layers in general and photographic gelatin-containing layers in particular that perfectly adhere to a dimensionally stable polyester film by the use of a single ad hesive layer comprising a mixture of gelatin and of a chlorine-containing copolymer.

It is another object of the invention to improve the adhesion of the adhesive layer to the polyester film support by heating both at l80220C. A further object is the incorporation of additives into the adhesive layer coating composition, so that the polyester film support carrying the adhesive layer can be stretched to a sufficient degree and heat-setted at l80220C so as to obtain a dimensionally stable polyester film, the adhesive layer remaining completely clear during stretching and heat-setting.

According to the invention a process is provided for improving the adhesion of hydrophilic layers to a dimensionally stable polyester film support, which process comprises applying, after longitudinal stretching of the polyester film support, a single adhesive layer thereto, stretching the thus covered polyester film support in transverse direction and heat-setting it at 220C, said adhesive layer comprising 30 to 80 70 by weight of a chlorine-containing copolymer, 5 to 30 by weight of gelatin, 5 to 40 by weight of a plasticizer for said gelatin as hereinafter defined, and O to 30 by weight of a metal complexing antistatic agent.

By plasticizers for gelatin according to the invention compounds are understood that are soluble or dispersible in water and photographically inert and that have the property of making layers formed from mixtures of gelatin and chlorine-containing polymers stretchable, these layers after having been stretched and heated at relatively high temperatures remaining completely transparent. The action of these so-called plasticizers is not only based on the known effects shown by external plasticizers, as described i.a. in the book Plasticization and Plasticizer Processes," Advances in Chemistry, Series 48 American Chemical Society, Washington DC. 1965. Probably this action results also in an improvement of the miscibility between gelatin and chlorine-containing copolymer, so that the chlorinecontaining copolymer in fact acts as a real external plasticizer for gelatin.

Suitable plasticizers are aliphatic polyhydroxy compounds such as glycerol, tri(B-hydroxyethyl)glycerol, 1, l l tri(hydroxy-methyl)propane, 2-nitro-2-ethyll ,3- propanediol, l ,3-dichloro-2-propanol, l ,2,4- butanetriol, 3-hydroxymethyl-2,4-dihydroxypentane, l ,2,6-hexanetriol, 2-hydroxymethyl-4-hydroxy-amyl alcohol, glycerobaldehyde, and mannitol.

Equally suitable compounds are caprolactam and N,N-dimethylurea. Other suitable plasticizers are aliphatic carboxylic or sulphonic acids such as glutaric acid, adipic acid, azelaic acid, sebacic acid monoand dichloro-acetic acid, 1,2,3-propene tricarboxylic acid, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and 2-sulpho-ethyl methacrylate; further aromatic acids such as phthalic acid, sulphobenzoic acid, o-nitrobenzoic acid, 0- aminobenzoic acid, p-hydroxybenzoic acid, and salicyclic acid. The chlorine-containing copolymers of the adhesive layer are copolymers comprising 70 to 95 by weight of vinyl chloride and/or vinylidene chloride, 0.5 to IO% by weight of a hydrophilic monomer, and 0.5 to by weight of at least one other copolymerizable monomer.

As copolymerizable monomers may be used esters of acrylic or methacrylic acid such as methyl, ethyl, butyl, hydroxyethyl, hydroxypropyl, glycidyl and cyanoethyl acrylate or methacrylate; further vinyl esters such as vinyl acetate and the vinyl ester of versatic acid, which is sold by Shell Chemical Co., under the trade name VEOVA l0 and is a branched chain vinyl carboxylic acid ester having a molecular weight of 198 and corre sponding to the formula:

wherein R., R and R are alkyl groups having together from seven to nine carbon atoms, and wherein only one of R R and R is a methyl group.

Other suitable copolymerizable monomers are acrylonitrile, acrolein and vinyl sulphofluoride.

The hydrophilic monomer may be taken from acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, the amides of acrylic and methacrylic acid, mono-alkyl esters of maleic acid, and vinyl pyrrolidone.

The chlorine-containing copolymer is added in latex form to the coating composition containing gelatin. This latex is obtained by the emulsion polymerization of the different comonomers according to known emulsion polymerization techniques. The so-called primary dispersion directly formed upon emulsion polymerization may be used as such, or after adaptation of its concentration. Greatly varying concentrations can be used depending on the final concentration and viscosity needed in the coating composition.

Suitable metal complexing antistatic agents are sulphosalicylic acid, 2,5-disulphohydrochinon, the sodium salt of ethylene diamine tetraacetic acid, ethanolaminodiacetic acid, the sodium salt of N(ohydroxybenzyl)-aminodiacetic acid, the monosodium salt of vanadic acid, 3,S-disulphopyrocatechin, phosphono-acetic acid, ethylene-l,2-diphosphonic acid, butylene-l,4-diphosphonic acid, and ascorbic acid.

To the coating composition of the adhesive layer may be added the known coating aids such as dispersing agents, spreading agents, antiseptic agents for the gelatin and thickening agents, which in general are highly viscous water-soluble polymers having as sole object to adapt the viscosity of the coating composition to the desired degree. A survey of the thickening of latices and of the thickening agents that may be used has been given by Houben-Weyl in Methoden der organischen Chemie, Makromolekulare Stoffe, Vol. 14/], pages 519 and 536, Georg Thieme Verlag, Stuttgart (l96l The chlorine-containing copolymer is added in the form of a primary dispersion and in the proportions indicated above to the aqueous gelatin solution, whereafter the plasticizer and possibly the antistatic agent are dissolved in water and mixed therewith. The viscosity of the coating composition thus formed is adapted as desired and known coating aids are added to the composition. Finally the coating composition is applied in known manner to a polyester film that has been stretched three to five times in but one direction, preferably longitudinally. After drying of the layer, the polyester film is stretched three to five times in a direction perpendicular to the first stretching direction, preferably transversally.

The coating composition for the adhesive layer is applied in such a ratio that after the second stretching operation a layer having a thickness between 0. l0 to 2 micron is obtained.

After the dimensional orientation of the polyester film by stretching in two perpendicular directions, the polyester film carrying the adhesive layer is conducted through a heat-setting zone, where it is heated at a temperature between l80 and 220C while keeping the film under tension in both directions. Hereby a dimensionally stable, completely clear polyester film is formed. Hydrophilic layers, such as gelatin-containing silver halide emulsion layers can be coated directly on the adhesive layer and will tenaciously adhere to this layer. The adhesion of the hydrophilic layer to the polyester film in dry as well as in wet state during the treatment of the photographic material in the different photographic processing baths is excellent.

The examples hereinafter are especially directed to the use of polyethylene terephthalate film as support for the adhesive layer and the hydrophilic layer or layers. The adhesive layer can, however, be applied to other polyester films, e.g. polyesters resulting from the polycondensation of glycol, or mixtures of glycols with terephthalic acid or mixtures of terephthalic acid with minor amounts of other dicarboxylic acids such as isophthalic acid, diphenic acid, and sebacic acid.

The invention is illustrated by the following Examples.

EXAMPLE 1 A substantially amorphous polyethylene terephthalate film having a thickness of approximatively 2.2 mm was formed by extrusion of molten polyethylene terephthalate at a temperature of about 280C on a quench drum and was chilled to a temperature of about 75C and then stretched in the longitudinal direction over a differential speed roll stretching device to 3.5 times its initial dimension at a temperature of 84C.

Upon the thus stretched film a layer was applied at a ratio of sq.m/litre from the following coating composition:

latex 335 ml l,l.ltri(hydroxymethyl)propane l2 g thickening agent l4.25 ml sodium salt of sulphosalicylic acid l0 g gelatin 5 g ULTRAVON W 5 ml [07: aqueous solution) water 633 ml The pH of the coating composition was adjusted to 8.2 with ammonia.

The latex used has a concentration of 20 by weight and was formed by the emulsion copolymerization of vinyl chloride, vinylidene chloride, n-butyl acrylate, and itaconic acid (63:30:5:2 by weight) such as described in United Kingdom Patent Specification No. 1,234,755 filed Sept. 28, I967 by Gevaert-Agfa N.V.

The thickening agent was the copolymer of ethyl acrylate and methacrylic acid (80:20 by weight). It was added in the form of an aqueous dispersion having a concentration of 20 by weight.

ULTRAVON W is the trade-name of ClBA AG, Switzerland, for a dispersing agent consisting of the disodium salt of heptadecyl-benzimidazole disulphonic acid.

After drying of the coating the film was stretched to 3.5 times in the transverse direction at a temperature of about 87C in a tenter frame. The final thickness of the film was about 0.180 mm.

The film was then conducted into an extension of the tenter frame, where it was heat-setted while kept under tension at a temperature of 200C for about 1 minute. After heat-setting the coated film was cooled and wound up in the normal manner.

The thus heat-setted film was treated with a corona discharge and was provided with a gelatin silver halide emulsion layer as used in photographic X-ray material. The layers of the photographic material thus obtained showed a very good adhesion to the polyester film support in wet as well as in dry state.

The adhesion in dry state was checked before and after the processing. The gelatin layer was scratched cross-wise by means of a sharp knife, whereafter an adhesive tape that was pressed thereon was torn off at once. The quality was approved only if but very small pieces of the photographic layer were torn off.

The adhesion in wet state was checked by scratching the material superficially and trying to rub off the gelatin layer with a finger after each step of the photographic processing (development, rinsing, fixing, rinsing). The gelatin layer should not be damaged during this rubbing.

EXAMPLE 2 The process of Example I was repeated with the difference that the longitudinally stretched polyester film was covered with the following coating composition at a ratio of 70 sq.m/litre:

latex 335 ml 3-hydruxymcthyl'2.4-dihydroxypcntane 5 ml gelatin g ULTRAVON W (scc Example I) 5 ml water 640 ml The latex also had a concentration of by weight, but this time it was obtained by emulsion polymerisation of vinylidene chloride. methyl acrylate, and itaconic acid (88: [0:2 by weight).

After transverse stretching and heat-setting as described in Example I a gelatin silver halide emulsion layer as used in photographic X-ray material was applied to the adhesive layer.

The layers showed good adhesion to the film support in dry as well as in wet state.

EXAMPLE 3 The process of Example 1 was repeated with the difference that the adhesive layer was coated from the following coating composition:

latex 350 ml gelatin 20 g l.l.l-tri(hyroxymethyl)propane 20 g water 610 ml The latex used had a concentration of 20 by weight and was obtained by emulsion polymerisation of vinyl chloride, methyl acrylate, and itaconic acid (88: 10:2 by weight).

Excellent adhesion of the gelatin silver halide emulsion layer in dry as well as in wet state was obtained.

EXAMPLE 4 In Example l the adhesive layer was formed from the following coating composition:

latex 350 ml gelatin 30 g 4-hydroxy-2-hydroxymethyl-amyl alcohol 25 g water 595 ml The latex is a copolymer of vinylidene chloride. vinylchloride, methylacrylate. and itaconic acid (58:30zl0z2 by weight).

Excellent adhesion of a lithographic photographic emulsion layer in dry and in wet state was obtained.

EXAMPLE 5 latex (as in Example 1) l ml gelatin 20 g l.2,4-trihydroxybutane 35 g water 770 ml Excellent adhesion of a photographic X-ray emulsion layer is dry and in wet state was obtained.

EXAMPLE 6 In Example 5 the adhesive layer was formed from the following coating composition:

latex (as in Example 2) I25 ml gelatin 20 g sodium salt of sulphosalicylic acid l0 g l,l.l-tri(hydroxy1nethyl)-propane 20 g Excellent adhesion of the hydrophilic layer in dry and in wet state was obtained.

EXAMPLE 7 The process of Example 1 was repeated with the difference that the longitudinally stretched polyethylene terephthalate film was covered with the following coating composition at a ratio of 70 sq.m/litre:

latex (as in Example 1 l 335 ml gelatin 6 g sodium salt of sulphosalicylic acid g n-sulphobenzoic acid 10 g water 640 ml EXAMPLES 8 AND 9 The process of Example 7 was repeated. In the coating composition, however, the o-sulphobenzoic acid had been replaced by a same amount of itaconic acid or of 2-sulphoethyl methacrylate. In both cases a photographic X-ray material was obtained, the layers of which showed excellent adhesion in dry as well as in wet state.

EXAMPLE 10 The process of Example 7 was repeated with the differcnce, however, that the o-sulphobenzoic acid was replaced by [5 g of glutaric acid and that the amount of water was 635 ml instead of 640 ml. Excellent adhesion of the layers in dry and wet state was obtained.

EXAMPLE 1 l The process of Example 7 was repeated with the difference, that the longitudinally stretched polyethylene terephthalate film was covered with the following coating composition at a ratio of 70 sq.m/litre:

latex (as in Example I l 420 ml gelatin 30 g sodium salt of sulphosalicylic acid 12 g adipic acid (as a 2t) 72 aqueous solution) 120 g ULTRAVON W H] .4 aqueous 6 ml solution water 574 ml A photographic X-ray material was obtained, the layers of which showed excellent adhesion in dry as well as in wet state.

We claim:

1. Process for improving the adhesion of hydrophilic layers on a dimensionally stable polyester film support, which comprises longitudinally stretching said polyes ter film, applying after longitudinal stretching of the polyester film support a single adhesive layer thereto, stretching the thus covered polyester film support in a transverse direction, and heat-setting it at l220C, said adhesive layer comprising 30 to 80% by weight of a chlorine-containing copolymer 5 to 30% by weight of gelatin, 4 to 40% by weight of a plasticizer for said gelatin, and from about 8% to about 30% by weight ofa sulphosalicylic acid salt as a metal-complexing antistatic agent, said chlorine-containing copolymer comprising about 70 to by weight of viny choride and/or viny]- idene chloride, about 0.5 to l0% by weight of a hydrophilic monomer, and about 0.5 to 25% by weight of at least one other copolymerizable monomer.-

2. The process of claim 1 wherein said gelatinplasticizer is an aliphatic polyhydroxy compound, an aliphatic carboxylic or sulfonic acid, or an aromatic acid.

3. The process of claim 1 wherein the amount of said composition is such that the adhesive layer after stretching and heatsetting has a thickness between about 0. 10-2 micron.

4. Process according to statement I, wherein the polyester film is a film of polyethylene terephthalatc.

5. Process according to claim 1,

wherein the chlorine-containing copolymer is a copolymer of vinylidene chloride, vinyl chloride, nbutyl acrylate, and itaconic acid (63:30:5:2 by weight).

6. Process according to claim I,

wherein the chlorine-containing copolymer is a copolymer of vinylidene chloride, methyl methacrylate, and itaconic acid (88: 10:2 7: by weight).

7. Process according to claim 1,

wherein the chlorine-containing copolymer is added to the coating composition of the single adhesive layer in the form of a primary dispersion in water directly obtained by the emulsion copolymerization of the difTerent monomers.

8. Process according to claim 1,

wherein the metal-complexing antistatic agent is the sodium salt of sulphosalicylic acid.

9. Process according to claim 1,

wherein the plasticizer is l,1,l-tri(hydroxymethyl)- propane.

10. Process according to claim 1,

wherein the plasticizer is taken from o-sulphobenzoic acid, itaconic acid, 2-sulphoethyl methacrylate,

and glutaric acid. 

1. PROCESS FOR IMPROVING THE ADHESION OF HYDROPHILIC LAYERS ON A DIMENSIONALLY STABLE POLYESTER FILM SUPPORT, WHICH COMPRISES LONGITUDINALLY STRATCHING SAID POLYESTER FILM, APPLYING AFTER LONGITUDINAL STRETCHING TO THE POLYESTER FILM SUPPORT A SINGLE ADHESIVE LAYER THERETO, STRETCHING THE THUS COVERED POLYESTER FILM SUPPORT IN A TRANSVERSE DIRECTION, AND HEAT-SETTING IT AT 180*-220*C, SAID ADHESIVE LAYER COMPRISING 30 TO 80% BY WEIGHT OF A CHLORINE-CONTAINING COPOLYMER 5 TO 30% BY WEIGHT OF GELATIN 4 TO 40% BY WEIGHT OF A PLASTICZER FOR SAID GELATIN, AND FROM ABOUT 8% TO ABOUT 30% BY WEIGHT OF A SULPHOSALICYLIC ACID SALT AS A METAL-COMPLEXING ANTISTATIC AGENT, SAID CHLORINE-CONTAINING COPOLYMER COMPRISING ABOUT 70 TO 95% BY WEIGHT OF VINY CHORDE AND/OR VINYLIDENE CHLORIDE, ABOUT 3.5 TO 10% BY WEIGHT OF A HYDROPHILIC MONOMER, AND ABOUT 0.5 TO 25% BY WEIGHT OF AT LEAST ONE OTHER COPOLYMERIZABLE MONOMER.
 2. The process of claim 1 wherein said gelatin-plasticizer is an aliphatic polyhydroxy compound, an aliphatic carboxylic or sulfonic acid, or an aromatic acid.
 3. The process of claim 1 wherein the amount of said composition is such that the adhesive layer after stretching and heat-setting has a thickness between about 0.10-2 micron.
 4. Process according to statement 1, wherein the polyester film is a film of polyethylene terephthalate.
 5. Process according to claim 1, wherein the chlorine-containing copolymer is a copolymer of vinylidene chloride, vinyl chloride, n-butyl acrylate, and itaconic acid (63:30:5:2 % by weight).
 6. Process according to claim 1, wherein the chlorine-containing copolymer is a copolymer of vinylidene chloride, methyl methacrylate, and itaconic acid (88:10:2 % by weight).
 7. Process according to claim 1, wherein the chlorine-containing copolymer is added to the coating composition of the single adhesive layer in the form of a primary dispersion in water directly obtained by the emulsion copolymerization of the different monomers.
 8. Process according to claim 1, wherein the metal-complexing antistatic agent is the sodium salt of sulphosalicylic acid.
 9. Process according to claim 1, wherein the plasticizer is 1,1,1-tri(hydroxymethyl)-propane.
 10. Process according to claim 1, wherein the plasticizer is taken from o-sulphobenzoic acid, itaconic acid, 2-sulphoethyl methacrylate, and glutaric acid. 